While Project 1A is aimed at identifying genes that are modulated by an acute fear conditioning paradigm, Project 1B is aimed at identifying genes that are differentially expressed in mutant mice that display variable levels of innate fear. The main difference between these two projects is that the first one studies learned fear while the second one studies innate fear. One disadvantage of innate fear over learned fear is that the underlying brain circuitry is less well understood. Therefore our first aim will be to identify which brain regions are controlling innate fear responses. To facilitate that dissection we have chosen to use as a starting point knockout mice that display increased anxiety-like phenotypes in tests of innate fear rather than selected inbred strains. In the knockout strains, the phenotype results from the absence of a single known gene. As a result the phenotype can be further dissected by using tissue-specific ablations of that same gene. In contrast, in inbred strains the phenotype is likely to result from the combined effect of many unknown genes which makes it much more difficult to assess the relevant brain regions. Another difference between projects 1A and 1B resides in the nature of the genes that will be identified in these two projects. In Project 1A, genes will be identified that are involved in the acute expression of fear in the normal adult brain; in contrast in Project 1B, we will attempt to identify genes that are differentially expressed either during development or in adulthood in the brains of "chronically anxious" mice. Whether these two gene pools are overlapping or not is unknown; however, both gene pools should provide candidates for the genetic determinants of anxiety disorders or anxiety-related traits (Projects 2, 3 and 4). The first goal of this project is to identify the brain regions and genes that are involved in innate fear responses. We will use knockout strains that rate high or low in tests of innate fear such as the 5-HT1A and the NK1 receptor knockout mice and we will use tissue specific and inducible knockout and rescue strategies to determine which circuits and developmental time periods are responsible for the anxious-like phenotype of these mouse strains. The second goal of this project is to compare these animal models of innate fear to the models of learned fear studied in Project 1A. Specifically we will study the behavior of the various knockout and rescue mice in conflict tests and fear conditioning tests to establish whether there is a correlation between these two types of anxiety-related paradigms. These studies parallel the human studies aimed at establishing correlations between neuroticism, behavior in fear conditioning paradigms, and anxiety disorders (projects 3 and 4). The third goal of this project will be to identify candidate downstream effector genes of the 5-HT1A or NK1 receptors. To achieve this goal, we will perform gene expression profiling using mRNA of wild-type and knockout mice from the critical tissues and time periods identified in aim 1. From this list of genes, we will select for further study those candidates whose expression is altered in the knockout and rescue mice in a way that correlates with their anxiety-like behavior.